ATM is a fast packet/cell switching technology used to transmit voice, data, image, and video signals. All broadband transmissions, whether audio, data or video, are divided into a series of fixed length cells and routed across an ATM network connected by ATM switches.
ATM technology is a connection-oriented protocol based on a standard 53-byte cell. The first five bytes carry control information and are referred to as the "header" of the ATM cell. The remaining 48 bytes carry user information or data. A virtual connection (VC) between end users must be set up before the end users can send information to each other. This is in contrast to a connectionless-oriented protocol, wherein a temporary virtual connection is established on demand when information is to be transferred.
Two of the key elements in the header of the ATM cell are known as the "Virtual Path Identifier" and the "Virtual Circuit Identifier." These are abbreviated as VPI and VCI, respectively. The VPI or VPI/VCI together "identify" an ATM cell (i.e., the address of a cell), and determine the "routing" of the cell within an ATM switch or a router. For additional information on ATM technology and details of how these fields are used to uniquely identify a cell as well as how they are used to route a cell in a switch or router, see the ITU-T or ATM Forum Standards.
ATM networks typically do not allow simultaneous transmission of high bandwidth information in a multipoint-to-multipoint two-way connection. This restricts the use of ATM networks in applications where several users would like to send and receive, simultaneously, video, image or data information and compare and contrast such information. For example, medical technology applications include situations where transmitters of information are located in different parts of the world, and receivers of information desire to compare/contrast images and video signals in real time.
Various attempts have been made to increase the amount of information which can be transmitted on a VC. Up to this point, implementations encompass the idea of a "frame merge", which interleaves traffic from different users at the frame level (rather than at the cell level). To implement a frame-merge, an ATM switch at the merge point stores incoming cells until an entire packet has arrived within the switch. The switch will then send the entire packet to the merged VC, while at the same time preventing any other user from transmitting information on the same merged VC. This approach has several disadvantages, including sophisticated channel control design requirements, extensive hardware resource requirements (e.g., buffers in the ATM switches), and the failure of this type of "store and forward" approach to carry real-time traffic. The frame-merge approach is simply impractical for real-time transmission of multimedia data over a label-switched Internet Protocol (IP) network.
Therefore, there is a need for a traffic merging network and method of operating a network that provides for merging information at less than the frame level. However, to be practical, this need must be solved by a network and method which are supported by current ATM switch hardware. Such a network and method will allow transition from current practices to the more efficient approach even before a specific operating standard is implemented. Such an approach will have many advantages over the hardware-based frame-merge solution.